This invention relates essentially to a tuning arrangement for a resonance module, and particularly to a tuning arrangement for making a separate tuning of a resonance module for a wireless application, e.g. for wireless communication, for example in a base station for a mobile telephony system, the base station having a plurality of resonance modules (cavities), each of them being automatically controlled to its given resonance mode in relation to the frequency of an incoming signal and thus being provided with a separate tuning arrangement, below called measurement receiver.
Since the mobile telephony systems are getting more and more complicated due to demands to carry more and more information and to be more and more frequency effective the modulation wave-form has become very complex. Tuning algorithms for auto-tuning of combiners have to be very advanced in order to function properly.
U.S. Pat. No. 5,408,688 describes a mobile telephone system including base station with a plurality of resonance modules. Each module is to be separately adjusted to its own frequency for receiving and expediting telephone signals at this frequency. Tuning is controlled to its given resonance position in relation to the frequency of the incoming signal. This is done by a drive connected for obtaining drive voltage by phase comparison. When the phase is calibrated it goes through zero, as apparent from the curve B in FIG. 3 in U.S. Pat. No. 5,408,688. The demand is then that both the input and output ports and the wiring are carefully calibrated, otherwise it is not possible to have a minimum attenuation when the phase passes through zero. The calibration operation is quite difficult. This kind of system can not handle the varying power levels within the time gaps of today. Such demands were not actual at the filing date of that patent.
The measurement receiver currently in use only measures the output signals of the resonance module. Therefore it is impossible to decide whether the change of power level depends on the actual tuning algorithm or on the modulation wave-form. The modulation wave-form of today has a power variation within the time gap, particularly in the modem TDMA systems, and it is expected that new systems to come have a further more variation within the time gap. Fast and accurate auto-tuning has therefore become impossible with the prior art systems.
An object of the invention is to provide an apparatus for making a fast and accurate auto-tuning of a resonance module.
Another object of the invention is to provide an apparatus for making an automatic and yet reliable tuning operation of a resonance module.
The objects above are solved by using an apparatus having the features in the characterizing part of claim 1. Further features and developments are disclosed in the rest of the claims.
The invention relates to a tuning arrangement for tuning a resonance module for wireless applications, e.g. for wireless communication, for example for a mobile telephony system, comprising means for deriving the input and the output power signals of the resonance module. The arrangement is characterized by means for dividing information bearing parts of the derived power signals with each other to have a ratio of them, and means for tuning the resonance module until the ratio has reached a minimum value. In this way the variation of the input and output of the resonance module cancel each other. An oscillator means is preferably setable to a frequency region adapted to the resonance module. A power detection and frequency counting means is preferably connected to derive the frequency and power of the input signal of the resonance module and set the oscillator means based on the output of the power detection and frequency counting means. First and second mixing means mix the derived input and the derived output, respectively, of the resonance module with an output of the oscillator means. A first filtering means filters the output of the first mixing means. A second filtering means filters the output of the second mixing means. A dividing unit to which the outputs of the filters are fed to an input each makes the ratio between its inputs to create an output being a signal independent of the signal variation of the input and output of the resonance module. A processing means makes a reciprocating adjustment of the resonance module until the output of the dividing unit lies on a minimum value.
By implementing a dual channel measurement receiver, i.e. a receiver which measures the input and the output of the resonance module coherently and computes their ratio, it is possible to deduce a signal which is proportional to the attenuation of the resonance module cavity. Any influence of the modulation scheme will be suppressed, since the output signal from the measurement receiver is the ratio of the input and output signals of the resonance module independently of any modulation wave-form. Hence the performance to the auto-tuning is improved significantly.
By using the principles according to the invention it is possible to provide a tuning operation on a mobile telephone system having power control per time gap, i.e. to handle varying power levels of the signal within the gap. This means during a time of ca some xcexcsec, for example 3 à5 xcexcsec, for a call in for example a TDMA system (TDMA=Time Division Multiple Access) and for future systems to come.
The measurement principle according to the invention to use a dual channel measurement receiver also eases the demands on the advanced tuning algorithms of today.